Vegetable Root Diseases from a talk by Linda Gilkeson

Vegetable Root Diseases:  Getting to the Root of the Problem

Presentation by Linda Gilkeson at

Vancouver Master Gardeners Spring Affair March 12, 2017

Notes by Shirley Cole and Sharon Shultz

• Hard to diagnose e.g. Garlic root diseases
  
• Focus on:  
  • What is the difference between disease tolerant, resistant and immune?
  • Tolerant - plant can still get disease but will still produce
  • Resistant - less likely to get disease or only minor infection
  • Immune - won’t be infested (rare)
    
  • Sanitation is very important to remove pathogen spread
  • Don’t wear garden boots/shoes to other gardens
  • Do not compost rogue or infected plants
  • Sanitize tools and containers
    
  • Crop rotation
  • is an effective way to control for many root diseases
  • Works by starving pathogens
  • Need to know what plants are in same families
  • Need to know other host plants for pathogens
    
  • Plants that are at low risk for root diseases are:
  • Goosefoot family
  • Sunflower family
  • Valerian family
  • Grass family
  • Gourd family
  
  
  
  
  
  
  • Root zone microbes - plants intentionally leach sugars and carbs to feed microbes and keep them around
    
  • Healthy soil community
  • Minimize cultivation
  • Leave roots in soil when cleaning up (don’t pull out plants, cut at soil level and keep roots in place)
  • Cover cropping
  • Add organic material - compost, green manure crops, surface mulch
    
  • Fungi
  • Largest group of pathogens
  • Threadlike filaments (hyphae) for a mass (mycelium)
  • Spores (much like seeds)
  • Schlerotia - contain food reserves  and remain dormant until conditions favourable
    
  • Five common groups of pathogenic fungi
  • Botrytis Neck/Bulb Rot
  • Affects alliums
  • Very common
  • 9 degrees Celsius needed for germination
  • Rot starts at neck or top of bulb
  • Warm/wet soil
  • Excessive nitrogen
  • Overwinters on plant debris
    
  • Basal Rot
  • Affects garlic, leeks
  • Cereals can host garlic strains
  • Spores are in most soils
  • Wet soils and late season favours this disease
  • Lesions with reddish edge
  • White fluffy mold
  • Crop rotation will help
  • Likes warm soil
    
  • Blue or Green Mold Rot
  • Affects garlic and elephant garlic - rarely onions
  • Suppressed in wet soil
  • Blue-green to brownish - first at base of bulb
  • Crop rotation for 2 years is often effective
    
  • Skin Blotch (Embellisia)
  • Recently introduced disease
  • Infects garlic
  • Mostly cosmetic damage
  • Spreads on the wind
    
  • White Rot
  • Remains in soil for more than 20 years WOW!
  • Remains dormant and germinates when it detects the roots of the onion/allium family
  • Can infect all alliums
  • Ideal conditions are temperatures less than 22 degrees Celsius, moist soil, infection inhibited above 24 degrees Celsius or 75 degrees Fahrenheit
  • Positive ID is hard - needs to be done by a plant pathologist.  You can send sample to Plant Health Laboratory, BC Ministry of Agriculture 1-800-661-9903 or PABH@gov.bc.ca.  Cost is about $16.
    
  • Prevention of White Rot
  • Use clean stock
  • If your garlic is good, use it for seed instead of bringing seed garlic.
  • Grow onions from seeds.
  • Clean rental equipment like roto-tiller (before use)
  • Promptly remove failing plants
  • Send sample to lab
  • Clean tools
  • Do not plant any more alliums
    
    
    
  • Prevention of Botrytis, Blue-Green Mold, or Basal Rot
  • 4 year crop rotation
    
  • Proper curing of garlic bulbs
  • Lift bulbs
  • Arrange in tray one layer deep
  • Dry for 3 weeks in warm & airy location
  • Store in dry & cool location
    
  • Potato Scab
  • Caused by filamentous bacteria
  • Often comes from using table/grocery store potatoes as seed.  Potatoes can be sold for consumption even if they show signs of scab.  So, grocery store potatoes may have scab.
  • Most severe in warm, sandy, dry soil
  • Don’t try to manage by changing pH
  • Manage by rotating crops
    
  • Soft Rot (Erwinia)
  • Bacteria root rot
  • Leave carrots in ground with lots of good mulch over top is the best storage
  • Prevention
  • Well drained soil
  • Avoid growing overwintering crops where soil is waterlogged
  • Practice good sanitation
  • Manage pests
    
  • Clubroot of Cabbage
  • Resting spores last 4 - 20 years in soil
  • Dormant spores activate when they sense the roots of cabbage family plants
  • Roots develop tumors
  • Thrives in moderate, wet, acidic soils
  • Huge range of host plants - they can carry the clubroot but can be asymptomatic
  • Susceptibility (Source:  Gilkeson, LInda. Resilient Gardens 2016:  Climate Change, Stress Disorders and Pest Update.  Self published.  2016. P. 55-57)
  • Most susceptible - cabbage, chinese cabbage, brussel sprouts, kohlrabi, kale, cauliflower, collards, broccoli, rutabagas, seakale, some cultivars of turnip & radish - also candytuft and wormseed mustard (Erysimum cheiranthoides), a widespread weed
  • Mildly susceptible - canola, black mustard, some turnips and radishes and tumble mustard (an introduced weed Sisymbrium altissimum)
  • Resistant  or immune - wintercress, horseradish, shepherd’s purse, wallflower, dame’s violet, peppergrass, garden cress, stocks and some radish cultivars.
  • Clubroot spores can also infect fine root hairs of some grasses, including redtop (Agrostis stoloniferae), orchardgrass (Dactylis glomerata) and ryegrass (Lolium perenne).  Clubroot can infect strawberry, red clover, corn poppy, dock (Rumex spp.) and mignonette.  Infections in these plants don’t show the swollen root tumours, but these host plants allow clubroot organisms to survive and build up spores in the soil.
    
  • Management
  • Lime to get higher pH (above 7.2)
  • 5-7 year crop rotation
  • Practice good sanitation between garden beds (if possible, use a separate set of tools for affected bed)
  • Can use bacillus subtilis (Natria)
  • Natural occurring bacteria
  • Seems to shield roots from infection
  • Use clubroot tolerant cultivators are more readily available